The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few invertebrates such as sponges, jellyfish, adult sea squirts and starfish do not have one, even if diffuse neural tissue is present. It is located in the head, usually close to the primary sensory organs for such senses as vision, hearing, balance, taste, and smell. The brain of a vertebrate is the most complex organ of its body. In a typical human the cerebral cortex (the largest part) is estimated to contain 15–33 billion neurons, each connected by synapses to several thousand other neurons. These neurons communicate with one another by means of long protoplasmic fibers called axons, which carry trains of signal pulses called action potentials to distant parts of the brain or body targeting specific recipient cells.
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Famous quotes containing the word brain:
“Knowledge of Rome must be physical, sweated into the system, worked up into the brain through the thinning shoe-leather.... When it comes to knowing, the senses are more honest than the intelligence. Nothing is more real than the first wall you lean up against sobbing with exhaustion.”
—Elizabeth Bowen (18991973)
“My brain sang
a rhythm I never dreamt to sing,
I will be gay and laugh and sing,
he is going away.”
—Hilda Doolittle (18861961)
“All science requires mathematics. The knowledge of mathematical things is almost innate in us.... This is the easiest of sciences, a fact which is obvious in that no ones brain rejects it; for laymen and people who are utterly illiterate know how to count and reckon.”
—Roger Bacon (c. 1214c. 1294)